Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$28.78	9.755%	$31.5875	$31.59	$31.60	$31.60
Purchase #2	$139.65	3.285%	$144.2375	$144.24	$144.25	$144.20
Purchase #3	$57.46	5.415%	$60.5715	$60.57	$60.55	$60.60
Purchase #4	$180.38	12.793%	$203.456	$203.46	$203.45	$203.50
Purchase #5	$107.83	3.316%	$111.4056	$111.41	$111.40	$111.40
Purchase #6	$215.41	5.711%	$227.7121	$227.71	$227.70	$227.70
Purchase #7	$133.26	6.855%	$142.395	$142.40	$142.40	$142.40
7 purchase totals =	$862.77		$921.3652	$921.38	$921.35	$921.40